Process for continuously preparing dyed filaments of acrylonitrile polymers



Dec. 6, 1969 KAZUM! NAKAGAWA ETAL 5 PROCESS FOR CONTINUOUSLY PREPARING DYED FILAMENTS OF ACRYLONITRILE POLYMERS Filed March 15, 1965 United States Patent US. Cl. 8--177 3 Claims ABSTRACT OF THE DISCLOSURE A process for continuously preparing dyed filaments of acrylonitrile polymer comprising: (a) wet-spinning an acrylonitrile polymer containing dye-receptive groups in the polymer structure to form wet gel filaments; (b) washing said wet gel filaments with hot aqueous liquid at a temperature higher than the subsequent dyeing temperature while under tension; (c) removing substantially all the surface liquid from the wet gel filaments; ((1) applying to the wet gel filaments a limited amount of dye solution containing a barely sufficient amount of dye to produce the desired shade; (e) holding the wet gel filaments with the dye solution thereon for at least ten seconds to permit substantially complete exhaustion of the dye from the dye solution; and (f) heat-treating the dyed wet gel filaments.

This invention relates to the continuous production of filamets of acrylonitrile polymer by a wet-spinning process which is modified to incorporate a novel sequence of steps for producing dyed filaments directly and continuously.

It is conventional to dye synthetic fiber after it is drawn and dried, but such a dried fiber is not only difiicult to dye, but it is especially difiicult to dye evenly. For this reason it is known to use a monomer that will increase the dye-receptivity of the fiber as a comonomer in the copolymerization reaction or to dye the fiber at high temperature in the presence of a wetting agent. In this connection, it is to be noted that U.S. Patent No. 2,558,- 735 describes a dyeing process in which fiber is dyed at the production step prior to drawing and drying where it is still in the gel state.

In the aforementioned processes, however, fiber may be dyed easily but not as evenly as may be desired. Stated differently, since the chemical nature of fiber is modified or a physical loose fiber is created in order to provide for increased dyeability, the dye-receptivity of the fiber may be increased but it is concomitantly rendered liable to develop unsightly stains or uneven dyeing.

In the production of any filament yarn, it is a matter of great importance to improve the evenness of dye reception. Also, when the fiber is to be dyed as part of the spinning operation, it must be completely dyed in a very short time. Therefore, the dye-receptivity of the fiber must be increased considerably. This, in turn, is necessarily accompanied by factors which adversely affect the evenness of dyeing.

In the production of synthetic fiber, and particularly filaments of acrylonitrile polymer by wet-spinning, there has been proposed, in the aforementioned US. Patent No. 2,558,735, a method of dyeing fiber in the gel state before it is dried. This invention provides an improvement on such process, using basic or acid dyes which permits dyeing the fiber evenly to a predetermined shade.

The term wet gel or gel state as used in this specification and the claims appended thereto means the state in which, after spinning and washing to remove the solvent, the fiber has not yet assumed its ultimate structure but still contains great amounts of water and, accordingly, remains swollen. This state disappears irreversibly upon drying so that the fiber assumes a compact structure. The latter structure, once it is established after drying, cannot be reconverted into the gel state, and this fact may be easily confirmed by a measurement of the moisture con tained in the fiber. Unless the fiber is dried, this gel state is not lost even after the fiber is washed and, then, stretched in hot water or steam.

We have noted that the water content of wet gel fiber is considerably reduced by heating it under tension in a hot, humid atmosphere. (In the process of our invention, this heating is preferably carried out at a temperature higher than the temperature at which the fiber will subsequently be dyed and, preferably, above 50 C.) This seems to indicate that the aforesaid gel state is made into a more compact gelled structure.

One of the important aspects of this invention lies in the possibility of retarding the dyeing rate of the dye onto the fiber and improving the evenness of dye reception by fiber by modifying the aforesaid gel structure to a certain extent. Furthermore, in the dyeing method of this invention, a traveling fiber is impregnated with a predetermined amount of a dyestulf in such a manner that the dye solution will not drip olf the traveling fiber. (In other words, the fiber is not impregnated with any excess amount of the dye solution.)

The fiber is held on and forwarded over thread-advancing rollers or a set of several other rollers in series, (generally, for at least 10 seconds), during which time the dye solution is exhausted. So that the dye solution taken up as above will not be removed from the gel fiber, it is necessary to remove the excess water from the fiber substantially completely by means of squeeze-rollers or by blowing the water off with the aid of air jets before the fiber is impregnated with the dye solution.

In the performance of our invention to achieve the aforesaid advantages we have found it important to remove excess water from the surface of the fibers after reducing the water content of the wet gel by treating with a hot aqueous medium. This removal of excess water may be by air jets or squeeze rollers prior to application of dye solution to the fibers.

After removal of surface water, dye solution is applied to thetraveling wet gel fiber which is held on and forwarded over thread-advancing rollers or a set of several rollers in series (generally for at least ten seconds), dur ing which the dye is exhausted onto the fiber. While the amount of dye solution which may be used without dripping varies with the size and number of individual filaments and the tension to which the fiber is subjected, it generally preferably lies within the range of from to 200% by weight based on the dry fiber.

For a clearer and more detailed description of the invention, reference may be had to the following descrip tion of specific embodiments read in conjunction with the accompanying drawing, the sole figure of which is a diagramatic view of an apparatus useful for the performance of the process of this invention.

Referring next to the drawing, continuously moving wet gel filaments F of acrylonitrile polymer are passed over and retained on thread-advancing rollers 1, 2 of conventional design where they are washed and heat-treated with hot water from shower 3. After washing, the surface water on wet gel filaments F is removed by means 4 which may be air jets or wringing rollers.

The wet gel filaments F, after removal of the surface water are forwarded to rollers 6, 7, 8 which comprise the equivalent of two sets of thread-advancing rollers. As the filaments F arrive at thread-advancing rollers 6, 7, dye

solution is padded onto the filaments F at a predetermined rae by means 5, such as a sponge or brush. After passing around thread-advancing rollers 6, 7 for sufiicient time to exhaust the dye solution (generally at least ten seconds), the filaments F are then passed around thread-advancing rollers 6, 8 where they are heated by means of internal electric heaters within roller 8. After leaving roller 6, the dyed, heated, wet gel filaments F may then be stretched in boiling water.

While it takes more than about ten seconds for the dye to be exhausted from the solution and combined with the fiber at room temperature, such rapid exhaustion frequently results in the uneven distribution of the dye among the filaments of which the yarn is constituted. Therefore, in order to prevent the occurence of uneven dyeing, the dye solution adsorbed on the yarn must almost instantly penetrate deep into the yarn so as to reach all filaments thereof, This extremely important, or no less important than, as mentioned hereinbefore, making the gel structure as compact as possible and, accordingly, reducing the dyeing rate. By removing as much water as possible from between the filaments before letting the dye solution be introduced, the dye solution is absorbed into the yarn the moment it is added so that the solution may penetrate deep into the yarn. Thus, the removal of water from the interstices between the filaments prior to the application of a dye solution is not only instrumental in preventing the dye solution from falling off the yarn but also conducive to avoiding uneven distribution of the dye among the filaments.

Even if the spun and washed gel fiber is processed to remove water from its surface, additional water gradually exudes out of the inner structure. Thus, the removal of the surface water is rendered futile. However, this trouble may be avoided if the gel fiber is heat-treated under tension in a humid atmosphere to reduce its water content prior to removal of surface water.

In order to disperse the adsorbed dye sufficiently deeply into the gel filaments, the dyed gel yarn may be held undisturbed at room temperature for about 10 seconds and then heated under roller tension for more than about seconds.

Just as in the heat-treatment under humid conditions which is carried out prior to the addition of said dye solution, a certain change in the gel structure is also observed when the fiber is heated in the course of dyeing. If the fiber is heated at a temperature higher than the temperature at which it was treated before the dye solution is added, additional water is removed from the interstices of the filaments, and as this occurs, some of the dyestuff may also be removed from the fiber, To prevent losses of the dye solution and promote the diffusion of the dyestuff, therefore, it is advisable to avoid using any substantially higher temperature than the temperature at which the fiber was treated prior to the addition of the dyestuff. And, as regards heating methods, it is preferable to heat the fiber with steam or a thermoelectric source, for instance, from inside the rollers in order that the dye solution may not be removed from the fiber. However, if some loss of the dye solution can be tolerated, one can blow steam against the fiber from outside.

The temperature at which the gel fiber is treated is above C. (preferably above C.), and the higher the temperature, the more satisfactory the effect of the heat-treatment, although the fiber will assume a somewhat milky appearance if it is treated at temperature over 80 C. While reductions in the dyeing rate vary with different types of dyestuff, this effect is generally satisfactory at temperatures over 80 C. Even when the gel fiber assumes a milky appearance due to the heat treatment at temperatures higher than 80 C., the physical properties of the final fiber are not appreciably inferior. The cross-section of the fiber is perfectly circular when in has been treated at high temperature over 80 C. while when dyed to a dark shade at low temperatures, the fiber is considerably distorted. This distortion occurs when. after dyeing, the fiber is stretched in steam or hot water. If the swelling of the gel fiber is held to a minimum, its distortion upon stretching occurs only in the direction of the fiber axis, yielding a smooth surface texture, but if the fiber is heat-stretched in a swollen state, the heat so used will cause dehydration of the fiber, with the attendant distortion thereof in the direction of its radius. This could raise the surface of the fiber, distorting its cross-sectional shape. Thus, by changing the temperature at which the fiber is heat-treated prior to stretching, it is possible to change, to a certain extent, the cross-sectional shape of the fiber from a perfect circle to substantially distorted shapes.

Since the dyeing method of the invention makes it possible to cause a given dyestuff to be absorbed evenly and completely into the fiber, the desired shade may be be obtained merely by mechanical control, i.e., by controlling mechanically the amount of dye to be added. It is to be noted, however, that the final shade may change due to the pH of the dye solution. Therefore, it will be necessary to use sufficient care in controlling the pH of the dye solution beforehand.

The dyeing method of the invention is particularly effective when a substantially complete dye exhaustion is desired. Satisfactory results will generally not be ob tained if the dye is not positively exhausted, or some of the dye remains adhered to the surface of the fiber or to the rollers being used in the spinning process, or part of the dye is removed from the fiber when it is washed or otherwise treated after the dyeing operation.

When the dye has been exhausted substantially completely the fiber may be immediately transferred from the dyeing step to a washing step and, accordingly, the impurities contained in the dyestuff may be removed. This washing step may of course be dispensed with if a dyestuff containing as little foreign matter as possible is employed, but it is advantageous, process-wise, to employ hot water at this washing step so that the effect of heating that would promote diffusion of the dye is secured at the same time.

One of the features of this invention lies in the fact that, even when a mixed dye consisting of two or more dyestuffs having dissimilar dyeing rates is employed, the problem of selective adsorption which is usually encountered in dip dyeing is substantially nonexistent.

One of the exemplary cases in which dyes are substantially exhausted is the case in which acrylonitrile polymers containing anionic polar groups, e.g., sulfonate, sulfate or carboxylate, or their alkali metal salts are dyed with basic dyestuffs. The case in which acrylonitrile polymers containing cationic polar groups such as pyridinium salts are dyed with acid dyestuffs is another example. When the fiber has dye sites at which it may form a salt with a dyestuff, the exhaustion of the dye occurs substantially positively, subject to the total chemical equivalent of said dye sites.

As has already been explained hereinbefore, with respect to the state in which dyes are rapidly exhausted, the fiber may be successfull dyed at room temperature if it has not yet been dried, and this is true if the fiber has already been heat-treated or heat-stretched. In view of the process involved, however, it is more advantageous to carry out the dyeing operation before the fiber is stretched, for a longer retention time may be had at this stage. Moreover, as stated hereinbefore, the dyeing of fiber before it is stretched is preferred also from a consideration of the processes of heat-treatment and washing after the exhaustion of the dye. Moreover, it is also possible to obtain the effect of washing by stretching the fiber in hot water.

To carry the method of this invention into practice, use may be made of the methods described in Japanese patent publication Nos. 3,645/ 1950 and 23,264/ 1963 for the production of acrylic synthetic fibers. However, even when other methods are employed, the dyeing method of this invention may be applied, when such methods produce fiber in a wet gel state in which it contains a high percentage of water and is swollen.

This invention is primarily carried into practice with the aim to avoiding uneven dyeing and making it easy to control the shade, but it becomes technically difficult to effect adsorption of the dye when the total denier number of the filament flowing through the process is too great and, in such cases, satisfactory results may not be obtained, especially in respect of the evenness of dyeing. The outstanding features of the invention come into effect primarily when it is applied to the spinning of fibers of less than 500 denier in terms of filament yam.

This invention will be better understood if reference is had to the following examples, it being understood, however, that the scope and spirit of the invention is by no means limited thereto.

EXAMPLE 1 Ten parts of a polymer (intrinsic viscosity: 1.70 DMF) containing 90%, 9% and 1% of acrylonitrile, methyl acrylate and sodium allysulfonate, respectively, was mixed with 90 parts of a 50% (by weight) aqueous solution of sodium thiocyanate, and the mixture was heated to prepare a uniform dope. The dope was spun into and coagulated by means of a 10% aqueous solution of sodium thiocyanate at C. to prepare a yarn composed of 50 filaments. The yarn was heated and washed on the apparatus shown in the accompanying drawing and then dyed under the following conditions:

Dyestufi: Astrazon Red F3BL (Cl. Basic Red 22) owf.

Gel fiber: 7.1 g. (dry weight)/min. (50 monofilaments) Cone. of dye solution: 3.55% (pH 3.5)

Amount of dye solution added: g./-min.

The adsorbed dye solution was taken from the gel fiber which had been held at room temperature for 10 and 30 seconds, respectively, and the amounts of exhausted dye were measured. The results are summarized in the following table, which also show the temperatures at which the gel yarns are heated and washed prior to the dyeing (the time of treatment is about 30 seconds) and the percent water contents of the gel yarns.

Water content of gel yarn after removal of surface Dye exhaustion, percent Heating and washing water, temperature percent 10 sec. 30 sec.

Room temp. 0.). 630 91 94 50 C 445 91 94 350 92 94 275 90 93. 5 180 87 93 130 83 89. 5

After the dye solution was applied, the yarns were held at room temperature for seconds. Then, the fibers were heated for about 30 seconds with the roller 8 indicated in the accompanying drawing (internal steam pressure: 0.1 kg./cm. The surface temperature of the roller was higher than 80 C. The fibers were then stretched 1000% in hot water and dried with drying rollers to prepare yarns having the total denier number of 150 denier.

The loss of the dye solution prior to thermal drawing was observed as the fibers were held at room temperature and, also, stayed on the heating roller at the heating-washing temperatures up to C. At temperatures of C. and higher, no substantial loss of the dye solution was observed. In all cases referred to in the above table, the cross section of fiber was roughly circular, and all the samples had been evenly dyed.

EXAMPLE 2 Fibers were prepared in the same manner as Example 1, except that the roller-heating after dyeing was dispensed with. In cases where the gel fibers were heated at C. and C., respectively, before dyeing, the crosssections of the fibers were almost circular and they were dyed in rings. Below 70 C., as the temperature is further lowered, the cross-sectional shapes of the fibers were more severely distorted, while the dye had penetrated into the cores of the filaments.

We claim:

1. A process for continuously preparing dyed filaments of acrylonitrile polymer comprising:

(a) wet-spinning an acrylonitrile polymer containing dye-receptive groups in the polymer structure to form wet gel filaments;

(b) reducing the water content of said wet gel filaments by washing with hot aqueous liquid at a temperature higher than the subsequent dyeing temperature while under tension;

(0) removing substantially all the surface liquid from the wet gel filaments;

(d) applying to the wet gel filaments a limited amount of dye solution containing a barely sufiicient amount of dye to produce the desired shade;

(e) holding the wet gel filaments with the dye solution thereon for at least ten seconds at room temperature or above but below the prior washing temperature to permit substantially complete exhaustion of the dye from the dye solution; and

(f) heat-treating the dyed wet gel filaments.

2. A process as defined in claim 1 wherein said washing step is performed with Water at a temperature above 50 C.

3. A process as defined in claim 2 wherein said step of heat-treating the dyed wet gel filaments is performed at a temperature lower than said washing step.

References Cited UNITED STATES PATENTS 2,558,735 7/1951 Cresswell 26428 GEORGE F. LESMES, Primary Examiner T. J. HERBERT, JR., Assistant Examiner US. Cl. X.R. 264-28 

